Data read/write systems comprising a tip

ABSTRACT

A method for writing data to and/or reading data from locations on a surface via a tip comprises moving the tip between the locations on the surface. At each location, energy is selectively applied to the surface via the tip and the tip and the surface are selectively forced together in synchronization with the application of energy.

CROSS-REFERENCE TO RELATED APPLICATION

This is a Divisional Application of U.S. application Ser. No. 10/472,021filed on Mar. 1, 2004, now U.S. Pat. No. 7,394,749 which is a nationalstage application claiming the benefit of International ApplicationPCT/IB02/00816 filed Mar. 15, 2002, which claims the benefit ofapplication number 01810296.2 filed with the European Patent Office(EPO) on Mar. 23, 2001, the disclosures of which are herein incorporatedby reference in their entirety.

BACKGROUND

1. Technical Field

The present invention generally relates to a method and apparatus forwriting data to and/or reading data from a storage surface via a tip.

2. Discussion of Related Art

An example of a such a storage device is described in “The“Millipede”—More than one thousand tips for future AFM data storage”, P.Vettiger et al., IBM Journal of Research and Development. Vol. 44 No. 3,May 2000. As described therein, this device comprises a two dimensionalarray of cantilever sensors fabricated on a silicon substrate. Eachcantilever is attached at one end to the substrate. The other end ofeach cantilever carries a resistive heater element and an outward facingtip. Each cantilever is addressable via row and column conductors. Therow and column conductors permit selective passage of electrical currentthrough each cantilever to heat the heating element thereon.

In both reading and writing operations, the tips of the array arebrought into contact with and moved relative to a storage mediumcomprising a polymer layer such as a layer of polymethylmethacrylate(PMMA) coating a plane substrate.

Data is written to the storage medium by a combination of applying alocal force to the polymer layer via each tip and selectively heatingeach tip via application of data signals through the corresponding rowand column conductors to a level sufficient to locally deform thepolymer layer, thereby causing the tip to leave an indentation or pit inthe surface of polymer layer. Conventionally, the local force is appliedby mechanically biassing the tip against the polymer layer. The storagemedium can be thermally erased and then rewritten multiple times. Toerase the storage medium, the polymer layer is heated to a levelsufficient reflow the polymer layer thereby removing all indentationsrecorded in the storage medium.

Each heating element also provides a thermal read back sensor because ithas a resistance which is dependent on temperature. For data readingoperations, a heating signal is applied sequentially to each row in thearray. The heating signal heats heating elements in the selected row,but now to a temperature which is insufficient to deform the polymerlayer. The thermal conductance between the heating elements and thestorage medium varies according to distance between the heating elementsand the storage medium. When the tips move into bit indentations as thearray is scanned across the storage medium, the distances between theheating elements and the storage medium reduce. The medium between theheating elements and the storage medium transfers heat between theheating elements and the storage medium. Heat transfer between eachheating element and the storage medium becomes more efficient when theassociated tip moves in an indentation. The temperature and thereforethe resistance of the heating element therefore reduces. Changes intemperature of the continuously heated heating elements of each row canbe monitored in parallel, thereby facilitating detection of recordedbits. Conventionally, relatively long tips have been employed in theinterests of achieving acceptable signal to noise ratios. However, suchlong tips are relatively delicate and difficult to manufacture. Also, inconventional devices, relatively soft polymers are employed in theinterests of ease of writing. However, a problem associated with suchmaterials in that deformations therein are relatively sensitive totemperature changes. Specifically, the deformations can be removed bychanges in environmental temperature, resulting in a corresponding lossof data. Additionally, as the array is scanned across the surface, thetips wear against the polymer material.

BRIEF SUMMARY

In accordance with the present invention, there is now provided a methodfor writing data to and/or reading data from locations on a surface viaa tip, the method comprising: moving the tip between the locations onthe surface; and, at each location, selectively applying energy to thesurface via the tip and selectively forcing the tip and the surfacetogether in synchronization with the selective application of energy.This arrangement improves reading and writing sensitivity.

The tip is preferably moved alternately towards and away from thesurface. This reduced wear on the tip as the tip is moved betweenlocations.

Further enhancements to reading and writing operations are achieved inpreferred embodiments of the present invention by selectively forcingthe tip and the surface together coincidentally with the selectiveapplication of energy to the surface via the tip.

Additional enhancements to reading and writing operations are achievedin particularly preferred embodiments of the present invention byoffsetting the selective applying of energy to the surface relative tothe selective forcing of the tip and surface together.

In preferred embodiments of the present invention, improved writingperformance is achieved by the selective applying of energy to thesurface comprising applying energy to the surface via the tip as the tipand the surface are moved towards each other. In particularly preferredembodiments of the present invention, further improvement in writingperformance is achieved by the selective applying of energy to thesurface comprising applying energy to the surface via the tipcoincidentally with the tip engaging the surface.

Similarly, in preferred embodiments of the present invention, improvedreading performance is achieved by the selective applying of energy tothe surface comprising applying energy to the surface via the tip as thetip and the surface are moved away from each other. In particularlypreferred embodiments of the present invention, further improvement inreading performance is obtained by the selective applying of energy tothe surface comprising applying energy to the surface via the tipcoincidentally with the tip disengaging the surface.

In especially preferred embodiments of the present invention, theselective forcing of the tip and the surface together comprisesselectively generating a force field acting on the tip to urge the tipand the surface together. Preferably, the tip is moved into and out ofcontact with the surface by the selective generation of the force field.The force field may comprise an electric field. Alternatively, the forcefield may comprise a magnetic field. In especially preferred embodimentsof the present invention, the energy comprises heat energy.

Viewing the present invention from another aspect, there is now providedapparatus for writing data to and/or reading data from locations on asurface via a tip, the apparatus comprising: a first transducersubsystem for moving the tip between the locations on the surface; asecond transducer subsystem for selectively applying energy to thesurface via the tip at each location; and, a third transducer subsystemfor selectively forcing the tip and the surface together insynchronization with the application of energy by the second transducersubsystem.

The third transducer subsystem preferably moves the tip alternatelytowards and away from the surface in synchronization with theapplication of energy by the second transducer subsystem. In preferredembodiments of the present invention, the third transducer subsystemselectively forces the tip and the surface together coincidentally withthe application of energy by the second transducer subsystem.

In particularly preferred embodiments of the present invention, theapplication of energy to the surface by the second transducer subsystemis offset relative to the selective forcing of the tip and surfacetogether by the third transducer subsystem. In such embodiments, thesecond transducer subsystem preferably applies energy to the surface viathe tip as the tip and the surface are moved towards each other by thethird transducer subsystem during writing operations. The secondtransducer subsystem may, during writing operations, apply energy to thesurface to the surface via the tip coincidentally with the tip beingbrought into contact with the surface by the third transducer subsystem.During reading operations, the second transducer subsystem preferablyapplies energy to the surface via the tip as the tip and the surface aremoved away from each other by the third transducer subsystem. The secondtransducer subsystem may, during reading operations, apply energy to thesurface via the tip coincidentally with the tip being moved out ofcontact with the surface by the third transducer subsystem.

In particularly preferred embodiments of the present invention, thethird transducer subsystem comprises a force field generator forselectively generating a force field acting on the tip to urge the tipand the surface together. The force field generator preferably moves thetip into and out of contact with the surface by the selective generationof the force field. The force field generator may comprise an electricfield generator. Alternatively, the force field generator may comprise amagnetic field generator.

The second transducer system preferably comprises a heater for applyingenergy to the surface in the form of heat.

The present invention also extends to a data storage device comprising astorage surface, a tip facing the storage surface, and apparatus forwriting data to and/or reading data from locations on the surface viathe tip as hereinbefore described. The preset invention further extendsto a data processing system comprising a central processing unit andsuch a data storage device connected to the central processing unit.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Preferred embodiments of the present invention will now be described, byway of example only, with reference to the accompanying drawings, inwhich:

FIG. 1 is a plan view of a sensor of a data storage device embodying thepresent invention;

FIG. 2 is a cross-sectional view of the sensor when viewed in thedirection of arrows A-A′;

FIG. 3 is an isometric view of the data storage device;

FIG. 4 is a cross-sectional view of a storage medium of the data storagesystem after a write operation;

FIG. 5 is a cross-sectional view of the storage medium after a selectiveerase operation;

FIG. 6 is another cross-sectional view of the storage medium after aselective erase operation;

FIG. 7 is an energy diagram of the surface of the storage medium;

FIG. 8 is a cross-sectional view of the storage medium during a writeoperation;

FIG. 9 is a cross-sectional view of the storage medium during aselective erase operation;

FIG. 10 is another cross-sectional view of a sensor of the data storagedevice;

FIG. 11A is a graph of spacing between the sensor and the storage mediumas the sensor is addressed to successive locations on the storagesurface;

FIG. 11B is a graph of write signals applied to the sensor at each ofthe successive locations;

FIG. 11C is a graph of read signals applied to the sensor at each of thesuccessive location; and,

FIG. 11D is a graph of a time varying electric field applied to thesensor at each of the successive locations.

DETAILED DESCRIPTION

Referring first to FIG. 1, an example of a data storage system embodyingthe present invention comprises a two dimensional array of cantileversensors 10 disposed on a substrate 20. Row conductors 60 and columnconductors 50 are also disposed on the substrate. Each sensor 10 isaddressed by a different combination of a row conductor 60 and a columnconductor 50. Each sensor 10 comprises a U-shaped silicon cantilever 15of a length in the region of 70 um and thickness in the region of micrometers. Limbs of the cantilever 15 are fixed, at their distal ends, to asilicon substrate 20. The apex of the cantilever 15 resides in a recess70 formed in the substrate 20 and has freedom for movement in adirection normal to the substrate 20. The cantilever 15 carries, at itsapex, a resistive heater element 30 and a silicon tip 40 facing awayfrom the substrate 20. The limbs of the cantilever 15 are highly dopedto improve electrical conductance. The heater element 30 is formed bydoping the apex of the cantilever 15 to a lesser extent, therebyintroducing a region of increased electrical resistance to current flowthrough the cantilever 15. One of the limbs of the cantilever 15 isconnected to a row conductor 60 via an intermediate diode 80. The otherlimb of the cantilever 15 is connected to a column conductor 50. Rowconductor 60, column conductor 70, and diode 80 are also disposed on thesubstrate 20.

Referring now to FIG. 2, the tip 40 is urged against a planar storagemedium in the form of a polymer layer 90 such as a film ofpolymethylmethacrylate (PMMA) of a thickness in the region of 40 nm. Thepolymer layer 90 is carried by a silicon substrate 100. An optionalbuffer layer 110 of cross-linked photo-resist such as SU-8 of athickness in the region of 70 nm is disposed between the polymer layer90 and the substrate 100. In both reading and writing operations, thetip 40 of the array is moved across the surface of the storage medium.In writing operations, the array of tips can be moved relative to thestorage medium to enable writing of data over an area of the polymerlayer 90.

Data is written to the storage medium by a combination of applying alocal force to the polymer layer 90 via the tip and applying energy tothe surface in the form of heat via the tip 40 by passing a writecurrent through the cantilever 15 from the corresponding row conductor60 to the corresponding column conductor 50. Passage of current throughthe cantilever 15 causes the heater element 30 to heat up. Heat energyis passed from the heater element 30 into the tip 40 via thermalconductance.

With reference to FIG. 3, each of the row conductors 60 is connected toa separate line of row multiplexer 180.

Similarly, each of the column conductors 50 is connected to a separateline of a column multiplexer 130. Data and control signals arecommunicated between a controller 210 and the row and columnmultiplexers 180 and 130 via control lines 140 and 150 respectively. Thestorage medium 90 can be moved in a controlled manner relative to thearray in orthogonal directions via positioning transducers 160, 170, and220. Transducers 160 and 170 effect movement of the array in a planeparallel to the surface of the polymer layer 90. Transducer 220 effectsmovement of the array in a direction perpendicular to the array. Inoperation, the controller 210 generates write signals for driving thearray during writing operations, read signals for driving the arrayduring read operations, and positioning signals for driving thetransducers 160, 170, and 220 to control movement of the tips in thearray relative to the surface of the polymer layer 90. The controller210 also receives outputs from the array during read operations. Inparticularly preferred embodiments of the present invention, transducers160, 170, and 220 are implemented by piezoelectric transducers,electromagnetic transducers, or a combination thereof. However, it willbe appreciated that other implementations are possible. The controller210 may be at least partially implemented by a microprocessor,micro-controller or similar control device or collection of controldevices. In some embodiments of the present invention, the transducer220 may be omitted.

With reference to FIG. 4, the write current is selected to heat the tip40 to a level sufficient to locally deform the polymer layer 90, therebycausing the tip 40 to indent the surface of the polymer layer 90 andleave a pit 120 of a diameter in the region of 40 nm. By way of example,it has been found that local deforming of a PMMA film can be achieved byheating the tip 40 to a temperature of the order of 700 degreescentigrade. The optional buffer layer 110 has a higher melting pointthan the PMMA film 90 and therefore acts as a penetration stop toprevent abrading of the tip 40 against the substrate 110. The pit 120 issurrounded by a ring 190 of polymer material raised above the polymerlayer 90. A second, overlapping pit 121 is shown in phantom dottedlines.

The heating element 30 also provides a thermal read back sensor becauseit has a resistance which is dependent on temperature. For data readingoperations, a heating current is passed though the cantilever 15 fromthe corresponding row conductor 60 to the corresponding column conductor50. Accordingly, the heating element 40 is again heated, but now to atemperature which is insufficient to deform the polymer layer 90.Reading temperatures of the order of 400 degrees centigrade are, forexample, insufficient to melt a PMMA film, but nevertheless provideacceptable reading performance. The thermal conductance between theheating element 30 and the polymer layer 90 varies according to distancebetween the heating element and the polymer layer 90. During a readingoperation, the tip 40 of is scanned across the surface of the polymerfilm 90. This is achieved by moving the array relative to the polymerfilm 90. When the tip 40 moves into a pit 120, the distances between theheating element 30 and the polymer layer 90 reduce. The medium betweenthe heating element 30 and the polymer layer 90 transfers heat betweenthe heating element 40 and the polymer layer 90. Heat transfer betweenthe heating element 30 and the polymer layer 90 more efficient when thetip 40 moves in the indentation 120. The temperature and therefore theresistance of the heating element 30 therefore reduces. Changes intemperature of the heated heating element 30 row can be monitored inparallel, thereby facilitating detection of recorded bits.

The aforementioned heating current is produced by applying a heatingvoltage pulse to the corresponding row conductor 60. Accordingly, aheating current flows through each sensor 10 connected to the rowconductor 60 to which the heating voltage pulse is applied. All theheating elements 30 in the corresponding row of the array are thereforeheated. Recorded data is then read out from in parallel from the heatedrow of sensors 10. Each row of the array is thus read sequentiallyaccording to a multiplexing scheme. In a preferred embodiment of thepresent invention, the storage medium provides a 3 mm.times.3 mm storagesurface.

Turning now to FIG. 5, recorded data bits can be selectively erased byforming new pits 121-124 overlapping each other over prerecorded data tobe erased to substantially level the surface of the polymer layer 90.This is achieved by performing the aforementioned write operation tooverwrite pits to be erased with a greater density of new pits 121-124overlapping each other so that each new pit effectively erases theimmediately preceding pit. Referring to FIG. 6, the overlapping new pits121-124 merge with each other and the pit to be erased 120 tosubstantially level the surface of the polymer layer 90. As mentionedearlier, the erasure need not be total. A series of ripples 200 may beleft in the surface of the polymer layer 90. It is sufficient that anerased bit is not detected as a data bit during a read operation. Thiswill of course depend on data reading sensitivity. The controller 210 isoperable in an erase mode to control formation of the new pits 121-124.Returning to FIG. 5, it may be acceptable in some applications for thelast new bit in a sequence written to erase an unwanted data sequence,such as the bit represented by new pit 124 for example, to form part ofa new data sequence to be recorded. In other arrangement, the density atwhich new bits are written to erase unwanted bits may be such that nonew bits remain recorded in the surface.

Referring to FIG. 7, the surface of the polymer layer 90 has a stable orground state 230 and a metastable state 240. Applying a combination offorce F_(w) and energy E_(w) to the surface via the tip 40 deforms thesurface into its metastable state 240 at the point of contact with thetip 40. With reference now to FIGS. 7 and 8 in combination, in apreferred embodiment of the present invention, a data bit written at alocation on the surface by positioning the tip 40 at the location andapplying a combination of force F_(w) and energy E_(w) to the surfacevia the tip 40 to deform the surface at the location. Referring to FIG.9, the data bit is then erased by positioning the tip 40 in deformationand applying energy E_(e) to the surface via the tip 40. Energy E_(e)may be less than that required to write a data bit onto the surface butgreater than that required to read a data bit recorded in the surface.Alternatively, energy E_(e) may be similar in magnitude to energy E_(w).Either way, energy E_(e) is sufficient to relax the surface from themetastable stable 240 to the stable state 230. In the erase operation,force F_(w) is reduced and may be removed altogether. The relief offorce F_(w) may be implemented via the transducer 220. With the forceF_(w) relieved, and energy E_(e) applied to excite molecules in thedeformed surface, intermolecular forces F_(m) in the surface aresufficient to push the tip 40 out as the surface relaxes into its stablestate. As indicated earlier, the different combinations of energy andforce required for reading, writing, and selective erasing operationsare provided to the array by the controller 210.

With reference to FIG. 10, in a preferred embodiment of the presentinvention, the substrate 110 is conductive and the controller 210comprises a voltage signal generator 250 which is selectivelyconnectable to each of the tips 40 of the array for selectivelyestablishing a potential difference between each tip 40 and the adjacentregion of the storage medium. The potential difference produces anelectric field E in the region of each tip 40. The electric field E isoriented to urge the tip 40 towards the surface of the polymer layer 90.The tip 40 thus applies an additional force to the surface of thepolymer layer 90 under the influence of the electric field E. Theadditional force can be employed to enhance both reading and, inparticular, writing operations. Specifically, the additional forcespermits higher data rates to be achieved in both reading and writingoperations. Experiments indicate that, in the nano-meter range, viscouscounter forces act against deformation of the surface of the polymerlayer 90 by the tip 40 at speeds greater than around 5 microseconds. Theadditional force imposed by the electric field E assists in overcomingsuch viscous forces. The effect of the E field is further enhanced byreducing the size of the tip 40. Experiments indicate that aconsiderable force can be locally imposed on the surface of polymerlayer 90 when the tip 40 is made considerably shorter than 1 micrometer.For such short tips, the capacitance between the sensor 10 and thesubstrate 100 is relatively high. For example, experiments indicate thata voltage of 10V imposed between the substrate 100 and a tip 40 oflength 100 nm imposes a force on the polymer layer 90 of around 0.1 mN.This force is strong enough to produce indentations in relatively softpolymers even when the tip 40 and the polymer layer 90 are at roomtemperature. In the absence of the electric field, the tip imposes aloading of around 0.0001 mN. Heating the tip 40 greatly reduces thepenetration time in the presence of the electric field E. Specifically,experiment indicates that the additional force provided by the E fieldbrings the data rate during writing operations into the nanosecondregime. Also, the combination of heating the tip 40 and applying theelectric field E increases flexibility in performing selective biterasing or overwriting operations. To write a bit and simultaneouslyerase neighboring bits, it is desirable to maintain the temperature ofthe tip 40 at a relatively high level. However, to write a bit and avoidsimultaneously erasing neighboring bits, it is desirable to maintain theforce applied to the polymer layer 90 via the tip 40 at a relativelyhigh level. Experiments indicate that a combination of the force imposedby the aforementioned electric field E and the heating of the tip 40 maylead to an increase in data storage density of a factor of 4. Withreference now to FIG. 11A, in a particularly preferred embodiment of thepresent invention, the tips 40 are lifted off the surface of the of thepolymer layer 90 between both successive reading operations andsuccessive writing operations. By way of example, FIG. 11A demonstratesthe variation in spacing d between a tip 40 and the surface of thepolymer layer 90 as the tip 40 is sequentially moved through successivepositions A to E on the polymer layer 90. d₀ indicates the spacing whenthe tip 40 is in contact with the surface. Positions A to E may beequidistantly or unequally spaced on the surface according to Thus,d₀=0. d₁ indicates the spacing when the tip 40 is furthest removed fromthe surface. The spacing d is controlled by the controller 210 via thetransducer 220.

Referring to FIG. 11B, in a write operation for writing data bits atpositions A to E, the controller 210 applies a write voltage pulse W₁across the heating element corresponding to the tip 40 as the tip 40impacts the polymer layer 90. The write voltage pulse W₁ produces acurrent flow in the heating element 30 of sufficient magnitude togenerate enough energy at the tip 40 to locally deform the surface ofthe polymer layer 90 in the region of the tip 40. Enhanced deformationof the surface of the polymer layer 90 is achieved via the tip 40impacting the surface from a remote position because additional energyis thereby imparted to the surface of the polymer layer 90. The enhanceddeformation improves the definition of the recorded data. As thesequence of positions A to E are written to sequentially, thecorresponding successive write pulses form a write signal W alternatingbetween an upper voltage level W₁ and a lower voltage level W₀. In someembodiments of the present invention, the write pulses W₁ may becoincident with the period for which the tip 40 is in contact with thesurface of the polymer layer 90. However, in particularly preferredembodiments of the present invention, the write pulse W₁ is skewedrelative to the period of contact between tip 40 and the polymer layer90 such that the write voltage is applied across the heating element 30prior to the time of impact of the tip 40 on the surface of the polymerlayer 40; continues to be applied into the period for which the tip 40is in contact with the polymer layer 90; and, is removed prior todisengagement of the tip 40 from the polymer material 90. The skewing ofthe write pulse relative to the contact period optimizes energy transferfrom the tip 40 to the surface of the polymer layer 90, therebyenhancing the extent of deformation of the surface of polymer surface.Referring to FIG. 11C, in a read operation for reading data bits atpositions A to E, the controller 210 applies a read voltage pulse R₁across the heating element corresponding to the tip 40 as the tip 40 isremoved from the polymer layer 90. The read voltage pulse R₁ produces acurrent flow in the heating element 30 of sufficient magnitude togenerate enough energy in the region of the tip 40 to permit detectionof variations in energy transfer corresponding to deformations in thesurface of the polymer layer 90. Detection of recorded data is enhancedby the forces at the surface of the polymer layer 90 acting inopposition to the disengagement of the tip 40 from the polymer layer 90.As the sequence of positions A to E are read sequentially, thecorresponding successive read pulses form a read signal W alternatingbetween an upper voltage level R₁ and a lower voltage level R₀. In someembodiments of the present invention, the read pulses R₁ may becoincident with the period for which the tip 40 is in contact with thesurface of the polymer layer 90. However, in particularly preferredembodiments of the present invention, the read pulse R₁ is skewedrelative to the period of contact between tip 40 and the polymer layer90 such that the read voltage is applied across the heating element 30during the period for which the tip 40 is in contact on the surface ofthe polymer layer 40 and is removed after the tip 40 is disengaged fromthe polymer layer 90 but prior to the next contact between tip 40 andthe polymer material 90. The skewing of the read pulse relative to thecontact period optimizes detection of data bits recorded in thedeformations of the surface of the polymer material 90.

It will be appreciated, that during the reading and writing operationhereinbefore described with reference to FIGS. 11A to 11C, the tips 40of the array remain in contact with polymer layer 90 for only arelatively short period of time (typically in the range of milli- tomicroseconds). This advantageously reduces frictional impediments to thelateral movement of the tips 40 relative to the polymer layer 100. Inaddition, this limits wear to the tips 40 otherwise produced byprolonged contact between the tips 40 and the polymer layer 90. Also,this reduces demand for uniformity and accuracy in the size of the tips40. A greater variation in spacing of the tips 40 and the polymer layer100 can be tolerated. This reduces manufacturing costs and improvesprocess yields.

With reference to FIG. 11D, in an especially preferred embodiment of thepresent invention, both reading and writing operations are enhanced byvarying the potential difference between the tip 40 and the substrate100 between voltages V₁ and V₀ via the voltage signal generator 250 ofthe controller 210. The voltage variations are synchronized to theperiods of engagement and disengagement of the tips 40 with the surfaceof the polymer layer 90. Specifically, the period of contact of the tip40 with the surface of the polymer layer 90 is timed to coincide withthe application of a voltage pulse imposed between the tip 40 and thesubstrate 110 by the voltage signal generator 250. The voltage pulseproduces an electric field E in the region of the tip 40. The electricfield E is oriented to urge the tip 40 towards the surface of thepolymer layer 90. The tip 40 thus applies an additional force to thesurface of the polymer layer 90 under the influence of the electricfield E. In a preferred modification of this embodiment of the presentinvention, the voltage pulses imposed between the substrate 100 and thetip 40 are coincident, during writing operations, with the writingpulses applied to tip 40 to enhance recording of data in the polymerlayer 90. Likewise, in another preferred modification of the presentinvention, the voltage pulses imposed between the substrate 100 and thetip 40 are coincident, during reading operations, with the readingpulses applied to the tip 40 to enhance reading of data recorded in thepolymer layer 90.

In the preferred embodiments of the present invention hereinbeforedescribed with reference to FIG. 11D, variations in a potentialdifference are imposed between the tip 40 and the substrate 100 incorrespondence with periodic engagement of the tips 40 with the polymerlayer 90. However, it should be appreciated that, in some embodiments ofthe present invention, the periodic variation of the potentialdifference between the substrate 100 and the tip 40 may be employedindependently of movement of the tip 40 relative to the polymer layer 90in a direction normal to the polymer layer 90. Specifically, in suchembodiments of the present invention, the voltage pulse imposed betweensubstrate 100 and tip 40 remain synchronized to reading or writingpulses applied to the tip 40 as desired operation dictates. However, thetip 40 remains in constant contact with the surface of the polymer layer90 as lateral movement of the tip 40 relative to the polymer layer 90 isproduced via the transducers 160 and 170.

Referring back to FIG. 10, is particularly preferred embodiments of thepresent invention, the area of the substrate is divided intoindividually addressable conductive zones. The voltage signal generator250 is selectively connectable to the zones via address lines formed inthe substrate 100. This enables the controller 210 to establish, via thevoltage generator 250 and the accompanying address lines, the electricfield E between a selected zone and a selected tip 40 or group of tips40. As mentioned earlier, the electric field E may be establishedbetween the substrate 100 and the heater element 30 of the tip 40.Alternatively, the electric field E may be established between thesubstrate 100 and a separate conductive platform integrated into thesensor 10 for generating the electric field E independently of theheater 30. Addressable conduction paths formed in or on the substrate 20and each connecting to a different one of the conduction platforms maythen be employed by the controller 210 to apply the electric field E toa selected tip 40 or group of tips 40. In other embodiments of thepresent invention, the electric field E may be replaced by a magneticforce field generated by selectively passing current through conductivecoils formed in or on the substrate 20 and the sensor 10 respectively.

To summarize the various embodiments of the of the present inventionpresented herein, a method has now been described for writing data toand/or reading data from locations on a surface via a tip comprisesmoving the tip between the locations on the surface. At each location,the tip and the surface are moved towards each other. Energy and forceare then applied to the surface via the tip. The tip and the surface arethereafter moved away from each other. In another arrangement describedherein, a force field is imposed in the region of the tip to urge thetip towards the surface.

1. A method for writing data to and/or reading data from locations on asurface via a tip, the method comprising: moving the tip between thelocations on the surface; at each location, selectively applying energyto the surface via the tip and selectively forcing the tip and thesurface together in synchronization with the selective application ofenergy; moving the tip alternately towards and away from the surface;and offsetting the selective application of energy to the surfacerelative to the selective forcing of the tip and surface together.
 2. Amethod as claimed in claim 1, wherein the selective applying of energyto the surface comprises applying energy to the surface via the tip asthe tip and the surface are moved towards each other.
 3. A method asclaimed in claim 2, wherein the selective applying of energy to thesurface comprises applying energy to the surface via the tipcoincidentally with the tip engaging the surface.
 4. A method as claimedin claim 1, wherein the selective application of energy to the surfacecomprises applying energy to the surface via the tip as the tip and thesurface are moved away from each other.
 5. A method as claimed in claim4, wherein the selective application of energy to the surface comprisesapplying energy to the surface via the tip coincidentally with the tipdisengaging the surface.
 6. A method as claimed in claim 1, wherein theenergy comprises heat energy.
 7. A method as claimed in claim 1, whereinthe selective forcing of the tip and the surface together comprisesselectively generating a force field acting on the tip to urge the tipand the surface together.
 8. A method as claimed in claim 7, comprisingmoving the tip into and out of contact with the surface by the selectivegeneration of the force field.
 9. A method as claimed in claim 8,wherein the force field comprises an electric field.
 10. A method asclaimed in claim 8, wherein the force field comprises a magnetic field.